This invention relates to a method for injecting a functional liquid such as a liquid crystal or an electrolyte solution into a display device cell having a relatively narrow space between two planar substrates held opposite to each other and to an apparatus for the same.
In producing a liquid crystal display device or an electrochromic display device, an indispensable and troublesome operation is injecting a liquid crystal or an electrolyte solution into the display device cell so as to fill the narrow space between the front and back substrates of the cell with the liquid crystal or the electrolyte solution. Several ways have been proposed for facilitation of this operation.
According to JP-A No. 48-77851, for instance, pressurized liquid crystal is forced into the display device cell by an inlet opening while another opening of the cell is used to discharge air and excess liquid crystal from the cell. However, this method is liable to leave bubbles at the interface between the liquid crystal and either of the front and back substrates of the cell. Besides, the provision of the two openings in the cell augments the probability of leakage of the liquid crystal or appearance of bubbles in the cell with the lapse of time. According to JP-UM-A No. 58-108431, for instance, vacuum is created in a display device cell to take in liquid crystal by utilizing a pressure difference. However, when this technique is applied to a large-sized cell a high vacuum has to be created in the cell so that the cell substrates are liable to be concavely distorted and may possibly be broken in the cases of glass substrates. Besides, it is likely that air is sucked in the cell at the time of sealing the inlet opening of the cell after taking in the liquid crystal. According to JP No. 59-34285 for instance, in producing a relatively large-sized liquid crystal display device liquid crystal is injected into the display device cell while the spacing between the front and back substrates of the cell is kept widened by disposing a spacer between the two substrates. This method is complicated and inconvenient for practical manufacturing.
According to JP-A No. 55-111919 for instance, an electrolyte solution is injected into an electrochromic display device cell by using a three-way manifold to evacuate the cell and then introduce the electrolyte solution into the cell. JP-A No. 57-129418 shows an apparatus for injecting an electrolyte solution into the cell of an electrochromic display device, including a vacuum chamber in which the cell is placed, a solution injection pipe which passes through a wall of the vacuum chamber and is held slidably movably and a pipe which is connected to the injection pipe at a section outside the vacuum chamber and extends to a vessel to receive a waste portion of the solution. These vacuum type methods and apparatus for electrochromic display device cells are still unsatisfactory from a practical point of view for several reasons including complexity of apparatus and operation and distortion of the cell substrates.